class Solution {
    int dx[4] = {0, 0 , -1, 1}; // i点加dx，dy就是i点的上下左右下标
    int dy[4] = {1, -1 , 0, 0};
    bool vis[51][51] = {false};
    int m = 0, n = 0;
 
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        m = grid.size(), n = grid[0].size();
        int ret = 0;
        for(int i = 0; i < m; ++i)
        {
            for(int j = 0; j < n; ++j)
            {
                if(grid[i][j] == 1 && !vis[i][j])
                {
                    ret = max(ret, bfs(grid, i, j));
                }
            }
        }
        return ret;
    }
 
    int bfs(vector<vector<int>>& grid, int i, int j)
    {
        int ret = 0;
        queue<pair<int, int>> q;
        q.push({ i, j });
        vis[i][j] = true; // 变成true就++ret
        ++ret;
        while (!q.empty())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int i = 0; i < 4; ++i)
            {
                int x = a + dx[i], y = b + dy[i];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == 1 && !vis[x][y])
                {
                    q.push({ x, y });
                    vis[x][y] = true;
                    ++ret;
                }
            }
        }
        return ret;
    }
};